1. Field of the Invention
The present invention relates to an epoxy resin composition for semiconductor encapsulating use, and a semiconductor device encapsulated with the resin. In particular, the present invention relates to the epoxy resin composition for semiconductor encapsulating use, excellent in the flowability, curability, moldability, and solder reflow resistance.
2. Description of the Related Art
Recent trends seeking a highly sophisticated electronic device while seeking the lighter, thinner, shorter and smaller electronic device promote higher integration technology and surface mounting technology of semiconductor devices. With the developments of such a technology, a requirement for epoxy resin composition for semiconductor encapsulating use becomes severer from day to day. Particularly, in low profiled type semiconductor devices, a stress arises due to an insufficient release of a cured epoxy resin composition from a mold for an encapsulating process. This stress may cause a crack in semiconductor elements in the semiconductor devices, or may lowered adhesion between the cured epoxy resin composition and the semiconductor elements at their interfaces. Furthermore, in surface mounted type semiconductor devices, lead-free solders become dominant instead of lead-containing solders, in view of ecological requirements. These lead-free solders require higher temperature for soldering. At such a higher temperature, a great stress is explosively arisen due to the vaporescence of the moisture contained in the semiconductor device. The solder reflow resistance capable of resisting such a great stress becomes a more serious concern than ever. Additionally, there is a need also for lead-free lead frames. From this viewpoint, in semiconductor devices, external plating with lead-containing solder is being replaced by a method using a pre-plating frame obtained by nickel plating, or gold plating on nickel/palladium alloy. The plating of pre-plating frame has remarkably low adhesion with the cured epoxy resin composition. Thereby, separation may be caused at the interface between the pre-plating frame and the cured epoxy resin composition, during the surface mounting. Therefore, there is a need for improving the solder reflow resistance.
In order to prevent the reliability from being lowered because of the soldering, or because of the semiconductor device using the pre-plating frame, there is proposed a technique which improves solder reflow resistance by making an epoxy resin composition with low hygroscopicity, high strength and low thermal expansion property by increasing an amount of an inorganic filler in the resin composition, and which maintains high flowability of the resin composition at a low viscosity during molding by using the epoxy resin composition having low melt viscosity (e.g. Japanese Patent Application Laid-Open No. Shou 64-65116, pages 2 to 7). By this technique, although the solder reflow resistance (may also be called “crack resistance”) is improved, the flowability is sacrificed by increasing an amount (content ratio) of the organic filler, so that voids are apt to be generated in the package. In view of this, there is proposed a technique which attempts to maintain the flowability by using a filler having various average particle sizes (e.g. Japanese Patent Application Laid-Open No. Hei 8-20673, pages 2 to 6). However, this method cannot provide an epoxy resin composition for semiconductor encapsulating use which has a good valance of the flowability and the solder reflow resistance.